Optical enhancement of phase modulation depth for a phase light modulator

Abstract

An optical architecture for enhancing phase modulation depth for a phase light modulator includes a laser light source, a 4f, 1:1 relay where a tilted mirror with a center hole is placed at the backfocal point of the first lens. A vertically polarized (VP) and collimated light is deflected by a polarized beam splitter (PBS), followed by passing through a Quarter Wave Plate (QWP) that converts linear polarization (LP) to right circular polarization (RCP). Upon interaction of the RCP light with PLM, spatial phase is modulated by 2kd(i,j). PLM reflects and modulates phase of light while changing the handness of polarization from RHP to left hand circular polarization (LCP). The 2nd interaction with QWP changes polarization of light from LCP to horizontally polarized (HP) light. The mirror M1 is placed at a half of the Talbot distance from the PLM as described later. The reflected light by M1 is a HP light, therefore it goes through the PBS and is converted to RCP by the 3rd interaction with QWP. Finally the light is modulated by the PLM with the same phase modulation profile and reflected to the direction along the incident laser beam via QWP and PBS. After the laser beam is doubly modulated, the laser beam diffracted towards direction defined by the CGH pattern displayed on PLM. The diffracted beam is reflected by the mirror placed in the 4f 1:1 collimating optics followed by a collimating optics for beam steering.

What is claimed is: 
     
         1 . A phase light modulator for use in an optical system having a laser light source that emits light, comprising:
 a. a plurality of pixelated micromirrors each of which is selectively movable to vary height in the direction of incidence of the light, wherein variation of height of the micromirrors is represented by d(i,j) where (i,j) indicates location of pixel;   b. means for modulating the micromirrors in a pixelated manner, whereby upon reflection of light by such spatially variable height and pixelated mirrors, phase of light is modulated 2kd(i,j) where k is a light propagation constant in free space, 2π/λ.   
     
     
         2 . The phase light modulator of  claim 1 , wherein the range of d(i,j) is chosen so that maximum displacement of micromirror d(I,j)=d_max=λ/2, or 2π phase modulation, where lambda is wavelength of laser. 
     
     
         3 . An optical system for enhancing phase modulation depth for a phase light modulator, comprising:
 a. a laser light source;   b. a relay having first and second lenses;   c. a tilted mirror having a central hole formed therethrough positioned between the first and second lenes, whereby vertically polarized and collimated light is formed along a light path;   d. a polarized beam splitter positioned in the light path to receive and deflect the vertically polarized and collimated light;   e. a quarter wave plate positioned such that the light deflected by the polarized beam splitter passes therethrough and converts linear polarization light to right circular polarization light;   f. a phase light modulator positioned in spaced relation to one side of the quarter wave plate and able to receive the right circular polarization and convert it to left circular polarization light;   g. a mirror positioned in spaced relation to the other side of the quarter wave plate and a half Talbot distance from the phase light modulator, whereby the left circular polarization light reflected from the phase light modulator passes through the quarter wave plate thereby changing the light from the left circular polarization light to horizontally polarized light which then passes to and is reflected by the mirror where it goes through the polarized beam splitter and is converted to right circular polarization light by the 3 rd  interaction with the quarter wave plate.   
     
     
         4 . A method for enhancing phase modulation depth for a phase light modulator, comprising the steps of:
 a. generating a laser light source;   b. forming vertically polarized and collimated light is along a light path through passage of the laser light source through a relay having first and second lenses and a tilted mirror having a central hole formed therethrough positioned between the first and second lenes;   c. receiving and deflecting the vertically polarized and collimated light with a polarized beam splitter positioned in the light path to form a linear polarization light;   d. converting the linear polarization light to right circular polarization light with a quarter wave plate positioned such that the light deflected by the polarized beam splitter passes therethrough;   e. converting the right circular polarization light to left circular polarization light using a phase light modulator positioned in spaced relation to one side of the quarter wave plate;   f. passing the left circular polarization light through the quarter wave plate to convert it to horizontally polarized light;   g. placing a mirror on the other side of the quarter wave plate from the phase light modulator and at a half Talbot distance from the phase light, whereby the horizontally polarized light is reflected by the mirror where it goes through the polarized beam splitter and is converted to right circular polarization light by the 3 rd  interaction with the quarter wave plate; and   h. modulating the light by the phase light modulator with the same phase modulation profile and reflected to the direction along the incident laser beam via the quarter wave plate and polarized beam splitter.